Genesis 38:2-10

2There Judah saw a daughter of Shua, a Canaanite, and he took her [as his wife] and lived with her.

3So she conceived and gave birth to a son and Judah named him Er.

4Then she conceived again and gave birth to a son and named him Onan.

5Again she conceived and gave birth to still another son and named him Shelah. It was at Chezib that she gave birth to him.

6Now Judah took a wife for Er his firstborn; her name was Tamar.

7But Er, Judah’s firstborn, was evil in the sight of the Lord, and the Lord killed him [in judgment].

8Then Judah told Onan, “Go in to your brother’s widow, and perform your duty as a brother-in-law [under the levirate marriage custom]; [be her husband and] raise children for [the name of] your brother.”

9Onan knew that the child (heir) would not be his [but his dead brother’s]; so whenever he lay with his brother’s widow, he spilled his seed on the ground [to prevent conception], so that he would not give a child to his brother.

10But what he did was displeasing in the sight of the Lord; therefore He killed him also [in judgment].